The hypothesis that is being tested in this research project is that there exist abnormalities in the functional interactions of non-malignant T cells in patients with leukemia that may play a role in the pathogenesis of the disease. During the first year of the project, we completed our studies on the phenotypic characterization of T-cell subsets from 40 patients with B-cell chronic lymphocytic leukemia (CLL) and studied the immunoregulatory functions to B-cell responses of purified T4-\and T8-positive cells from five patients. These studies revealed a wide range of T-cell defects in patients with CLL. Our objectives for the second year of the project are: (1)\To continue our studies on the immunoregulatory properties of purified T4-\and T8-positivecells from patients with CLL and their interactions. A total of 20 patients will be studied. To analyze the population with suppressor function present in T4-positive cells from certain patients with CLL. To determine if abnormal T-cell functions are associated with hypogammaglobulinemia and other clinical parameters of CLL. (2)\To study T-T cell interactions between T4-\and T8-positive cells from patients with CLL during proliferative and cytotoxic responses to allogeneic cells in MLC. (3)\To study cell interactions between remission T lymphocytes and autologous leukemic cells from patients with acute lymphoblastic or myelogenous leukemia, during generation of "autologous leukemia-specific cell-mediated cytotoxicity" in "three-cell"-type mixed lymphocyte cultures. To determine the lymphocyte subpopulations that exhibit proliferative and cytotoxic responses to autologous leukemic cells as well as the cell surface phenotypes of effector cells. To determine the nature of the cell surface antigens on leukemic cells that elicit proliferative and cytotoxic responses by autologous T lymphocytes. It is expected that these studies will improve our understanding of these lymphoproliferative disorders and permit the design of more rational approaches for therapeutic and prophylactic management of the disease.